Known electric storage devices include, for example, lithium-ion batteries, nickel-hydrogen batteries and secondary batteries such as lead storage batteries, and electrochemical capacitors such as electric double-layer capacitors. The miniaturization of mobile devices or the limitation on setup space now requires further downsizing of electric storage devices, and attention has been paid to lithium-ion batteries whose energy density is high. As to the outer packaging materials used for lithium-ion batteries, although metal cans have been hitherto used, there are increasing uses of multilayer films that are light in weight and high in heat dissipation and can be made at low costs.
With the lithium-ion batteries using such a multilayer as mentioned above, such a configuration is adopted that battery contents (positive electrode, separator, negative electrode, electrolytic solution and the like) are covered with an outer packaging material including an aluminum foil layer in order to prevent the infiltration of moisture thereinside. The lithium-ion battery adopting such a configuration is called an aluminum-laminated type lithium-ion battery.
A known aluminum-laminated type of lithium-ion battery is, for example, an embossed type of lithium-ion battery wherein a recessed portion is formed at part of an outer packaging material by cold forming, battery contents are accommodated in the recessed portion, and the residual portions of the outer packaging material are folded back, followed by heat sealing the edge portions (e.g., see Patent Literature 1). With such a lithium-ion battery, a deeper recessed portion formed by cold forming enables the accommodation of a greater number of battery contents therein. Thus, a higher energy density can be realized.